1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, a semiconductor device generally means any device which can function by utilizing semiconductor characteristics, and an electro-optic device, a semiconductor circuit, and an electronic appliance are all included in the category of the semiconductor device.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor using a semiconductor thin film (also referred to as a thin film transistor (TFT)) formed over a substrate having an insulating surface. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor including a semiconductor layer formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) (In—Ga—Zn—O-based amorphous oxide) is disclosed (see Patent Document 1).